Hydraulic drive



April 4, 1944. R. E. DAVIS A HYDRAULIC DRIVE Filed March 4, 1940 INVENToR. Y Hlm-IARD EDM/|31 BY 4W W ATTORNEY.

' Patented Apr. 4, 1944 HYDRAULIC DRIVE Richard E. Davis, Wauwatosa, Wis., assigner to The Oilgear Company, Milwaukee, Wis., a corporation of Wisconsin Application March 4, 1940, Serial No. 322,099

(Cl. 6Il52) 12 Claims.

'I'his invention relates to hydraulic drives of the type employed for operating a machine having an element which is to be operated in op,

posite directions by the motor of the drive and which is constantly u rged in one direction by an independent force, such as the platen of a vertical press or the tool slide of a vertical broaching machine each of which is constantly urged downward by gravity.

A drive employed for this purpose ordinarily includes a resistance valve which resists the discharge of liquid from the motor during movement of the element in the direction in which it is urged by the independent force, and the resistance valve is so adjusted or proportioned that the pressure required to open it is higher than the pressure created inthe motor by the element being urged in that direction by the independent force, thereby enabling the motor to hold the element stationary when the machine is idle.

However, when the motor is operating the element in that direction to perform useful work, the energy expendedin forcing the motor discharge liquid through the resistance valve not be damaged if operated at such a temperature.

The present invention has as an object` to provide such a machine with a hydraulic drlve having means which will hold the platen, slide or other. element of the machine stationary when the machine is idle but which will not materially reduce the force available for 4performinguseful work or cause the liquid to become overheated.

Other objects and advantages will appear from the following description of an embodiment of the invention shown schematically in the accompanying drawing in which the views are as follows:

Fig. 1 is a circuit diagram of a hydraulic drive in which the invention is embodied.

Figs. 2, 3 and. 4 are views showingthe valves in positions other than those shown in Fig. 1.

For the purpose ofillustration, the drive has been shown provided with a reciprocating hydraulic motor consisting of a stationary vertical cylinder I and a piston 2 which is fitted in cylinder I and connected by a rod 3- to a carriage or slide 4 which may be the tool slide of a vertical broaching machine.

Motor i-2 is adapted to be energized by liquid supplied to the upper' and lower ends of cylinder I through two channels 5 and Ii respectively. The liquid may be supplied from a unidirectional pump to opposite ends of cylinder I alternately through an ordinary reversing valve but, since the displacement of the pump must be varied in order to vary the speed atwhich slide 4 moves the tools carried thereby across the work, a reversible pump is ordinarily employed as a reversing valve would only add te the cost of the machine.

.As shown, motor I-2 is energized by liqui'd supplied by a reversible pump 1 which delivers liquid into one or the other of two Vchannels 8 and Il to cause the motor to operate in one direction or the other and which draws its supply of liquid from a reservoir I0 through a check valve II during movement of piston 2 in one direction and is supplied with liquid from cylinder I during movement of piston 2 in the opposite direction as Willpresently be explained.

Since vthe volume of liquid discharged from cylinder I will vary from the volume delivered thereto by an amount equal to the displacement of piston rod 3, and since it is desirable to move slide 4 upward at a speed considerably higher than 4the speed at which it is moved downward, the drive has been shown as being provided with a differential valve consisting primarily of a valve casing I5 and a valve member I6 arranged there- Valve casing I5 encloses` a chamber I'Iwith which channel 5 communicates through a side wall thereof. Chamber I'l contains a boss I8 which is ordinarily formed integral with another side wall of casing I5 and has formed therein a bore I9 in which valve member I6 is slidably tted. Boss I8 has an annular groove 20 formed therein around bore I9 and connected by chan-- nel 2I to a relief valve 22 which discharges into reservoir ID, and valve member IB has a duct adapted to register with groove 20 in@ boss I8.

Bore I9 is'arranged in axial alinement with two bores 25 and 26 which are arranged in the opposite ends of casing I5 and have the same diameter as here i@ so that valve member i@ may be nttecl in here it) and either oi? bores 25 and 2t simultaneously. Bore has channel il connected thereto and bore 2t is connected by a channel 2l to channel s intermediate the ends thereof so that, when valve member it is in the position shown in his. l, channel il communicates through chamber il and channel 2l with channel t anni counication between channels t and il is blocked and,` when valve member l@ is in the position shown in lig. 2, channel t is connected to chael il through chamber il and channel Si is connected through channel il, duct 23, 'grooves te and il@ and channel 2l to relier valve l2.

The weight or slide and associated parts tends to move piston 2 downward and cause it to eject liquid from the lower end ci cylinder Il4 so that, ii channel t were connected directly to channel il, the pressure created in the lower part of cylinder i clue to the weight supported hy piston v2 would cause liquidi to lealr through the pump and thereby permit piston Q and slide d to move downward slowly when the machine was idle, it being understood that a sali amount of internal leakage is an inherent characteristic of all pumps.'

li when the machine is idle downward movement oi slide d were prevented luy connecting,1

a tree return `resistance valve hetween the low- J er end of cylinder i and the intake ci pump according to the usual practice, the entire volurne ci liquid expelled from' the lower part oi cylinder l would have to he forced through the resistance valve which would cause a waste of power and a large amount of heat to be gen-l crateri the liquid.

ln orcler to overcome the above objectionable features, a hydraulically operated resistance valve 3l is connected between channels t and t to prevent downward movement ci piston l when the .machine is idle and to permit substantially free riow of liquid when the machine is in operation.

Resistance valve Si has been shown as including a valve casingi having an axial bore @il formed therein and communicating at its upper end with an axial port @El having an annular valve seat formed around. the inner end thereof. Valve seat normally has a valve member in engagement therewith to control communication between port 35i and an annular port 3l which is formeel in the wall of the `tore at theupper enti thereof. Ports Sil and fil have channels 9 and il connected thereto, respectively,A so that valve member Se, controls communication between channels ti Aariel Valve member Se is connected to or formed integral with a plunger 3l? which is tted in here and urged upward by a light spring tu so that valve member tit is normally held in contact with valve seat to block communication hetween channels t and u. Valve member is smaller in diameter than plunger tu to provide therebetween a shoulder lil upon which liquid may act to move plunger downward and thereby move valve member away ltroni valve seat @to open communication between channels and The area of shoulder anti the tension of spring are so proportioned that a very low pressure, for instance per square inch, will exert suclent torce upon shoulder it to move plunger til downward and thereby move valve member tt out of contact with. valve seat aeaaaio Since when the machine is idle piston 2 will be urged downward hy the weight of slide fl and associated parts and since resistance valve 3l prevents piston 2 from electing liquid from the lower 'end of cylinder i, pressure will be created in the lower part or cylinder i and this pressure will act upon shoulder @il and tend to move plunger le and valve member t@ downward to open resistance valve 3i.

However, the same pressure is applied to the lower end of plunger'lt and, since the effective pressure area on the lower end ci plunger is greater than the effective pressure' area at the upper end thereof due to the area of valve member et which is open to port tl, the upward iorce exerted by the liquid exceeds the downwardorce exerted thereby so that valve meinber t@ is rmly held in contact with valve seat til Awhen the machine is idle.

The application of pressure to the lower end of plunger ilu is under the control of a pilot valve lh having three spaced apart heads or pistons do, ill and it formed thereon and closely tted in the here tu of a valve casing 5u. laiston il controls an annular groove or port which is formed in the wall of vhere le and connected by a channel til to the lower enel of here' 33 in valve casing That part oi bore all) hetween pistons iti and il is open at all times to the lower end of cylinder i as by being' connected hy a channel E53 to port ill in valve casing t2, and that part of bore it between pistons lll and 433 is connected to a drain channel ed. '.lhe lower end oi' bore d@ is connected hy a channel @l5 to channel 5 so that, when pump l ils-adjusted to deliver liquid to the upper end ci cylinder i to move piston l downward, lic,- uici will enter the lower end ci bore d@ and move valve it upward to the position shown in Fig. Ai. valve fit is urged downward by a spring arranged the upper end or bore dit but, in order that a light spring may he employed and to assure that valve @t will be positively moved downward at the proper point in a cycle oi operation, the upper end of here @le is ordinarily connected to channel 9 hy a channel t?? so that, when pump l is adiustecl to deliver liquid to the lower end of l cylinder i to move piston l upward, liquid will enter the upper end or here and move valve fili downward to the position shown in Fig. l.

When pilot valve is in the position shown in l, piston fil overlaps port lil and communication between port #El and channel El@ is provided hy a plurality ci small tapered grooves et which are lorrnel in piston el to throttle the iiow ol liquid to the lower enel oi here and thereby prevent plunger 323 irons advancing valve memher into contact with valve seat with such torce that damage might result. lin order .that .resistance valve ill may loe uuichly opened, a chech valve t@ is connecten between channels t2 and to permit liquid to esca freely from channel inw chael hut to prevent the how or liquid im the opposite direction except through the grooves tu.

@iteration lllhen the several are in the positions shown in l and pump l is iclle or at aero stroke, the weight of slide i and associated parte will tenol to move piston ii downward and cause it to eject liouid :troni the lower part of cylinder l hut spring 3Q will hold valve member against valve seat and prevent the escape of liquid so that the force exerted by piston 2 will create pressure in the lower part of cylinder I.

This pressure will extend through channel Ii to port 31 in valve casing 32 and tend to move plunger 38 downward by. acting upon shoulder 40 but it cannot do so for the reason that the same pressure will extend from port 31 through channel 53, bore 49 in valve casing 50, grooves 53 in piston 41, port 5| and channel 52 to the lower end of bore 33 in valve casing 32 and act upon the lower end of plunger 38 so that valve member 36 is held rmly in contact with valve seat 35, thereby positively preventing piston 2 and slide 4 from descending when the machine is idle.

'I'.o start the machine on a working stroke, pump 1 is adjusted to cause it to deliver liquid into channel 8. The liquid will shift differential valve member I6 to the position shown in Fig. 2 and then flow through chamber I1 and channel 5 to theupper end of cylinder I but the liquid in the lower part of cylinder I initially. prevents piston 2 from moving downward and thereby causes pump pressure to rise.

Liquid will then ow from channel 5 through channel 55 to the lower end of bore 49 in pilot Vvalve casing 50 and move pilot valve 45 upward .y lower end of bore 33 is destroyed. The pressure acting upon shoulder 40 will then move plunger 38 and valve member 36 downward and plunger 38 will expel liquid from the lower part of bore 33 through channel 52 and bore 49 into drain channel 544. Downward movement of valve member 39 opens communication between channels 6 and 9 so that piston 2 may expel liquid from the lower end of cylinder l. l

The liquid discharged by pump 1 will then flow through channel 8, chamber I1 in differential valve casing I8 and channel 5to-the upper end of cylinder I and move piston 2 downward on a working stroke, and piston 2 Awill expel liquid from the lower part of cylinder I through channel 6 and resistance valve 3I into channel 9. Since the volume of liquid discharged from cylinder' I is greater than the volume of liquid supplied to cylinder I by pump 1, a part of the discharge liquid will flow through channel 9 to the intake of pump 1 and the remainder will ow from channel 9 through channel 21, duct 23, grooves 24 and 20, channel 2I and relief. valve 22 into reservoir I0. -Relief valve 22 will resist the discharge of liquid therethrough and thereby cause pressure to be `createdin channel 9 so that pump 1 is supercharged at a pressure equal to the pressure required to open reliefV valve 22. The pressure required to open reliefvalve 22 is ordinarily substantially higher than the pressure required to compress spring 39 so that the force exerted by theliquid on shoulder 40 and valve member 36 will move valve member 36 far enough from valve seat 35 to provide free flow of liquid from channel 6 into channel 9. Consequently, the resistance to the discharge of liquid from the lower end of cylinder I is provided solely by relief valve 22 which is adjusted to provide in cylinder I a back pressure of the magnitude ordinarily employed for this purpose, for example, 300# per square inch.

While the pressure in the upper end of cylinder I must exceed the pressure required to perform useful work by `an amount equal to the back pressure, pump 1 need create only the pressure required to perform the useful work for the reason that it is supercharged by the back pressure.

For example, if a pressure of 1000# should be required to perform the useful work and the back pressure should 'be 300#, a pressure of 1300# would be required in the upper end of cylinder I to move piston 2 on a working strokebut, since pump 1 is supercharged by the back pressure, it would only have to raise the pressure from 300# to 1300# or a diierence of 1000# and, since the volume of liquid exhausted through relief valve 22 is relatively small for the reason that the ratio of the area of cylinder I to the area of piston rod 3 is ordinarily five or six to one, the power loss at relief valve 22 is relatively small and the amount of heat created in the liquid is so small that it is readily dissipated.

If piston 2 had connected thereto a second rod which had the same diameter as rod 3 andv extended through the lower end of cylinder i or if the invention were applied to a downward acting hydraulic 4press in which the ram or piston rod extended through the lower end of the cylinder, differential valve I5-i6 and relief valve 22 would be omitted in which case the apparatus would function in the above described manner to positively. hold the piston stationary when the machine was idle but would cause no power loss whatever during a working stroke of the piston.

After piston 2 has completed its working stroke, pump 1 is adjusted to deliver liquid into channel 9,'thereby causing pressure to be created therein and the pressure in channels 5 and 8 to drop substantially to zero so that differential valve member. I6 is moved to the position shown in Fig. 1 by pressure extending from channel 9 through channel 21, and pilot valve 45 is moved downward to the position shown in Fig. 1 by spring 55 or by pressure extending from channel 9 through channel 51 to the upper end of bore 49.

The liquid delivered by pump 1into channel 9 will move resistance valve member 36 downward and then flow through ports 34 and 31 and channel 6 to the lower end of cylinder I, downward movement of valve member 36 being resisted only by spring 39 for the reason that plunger 38 can expel liquid from the lower part of bore 33 through channel 52, check valve 59 and channel 53 into port 31.

The liquid delivered by pump 1 to the lower end of cylinder I will move piston 2 upward and cause it to expel liquid from the Iupper end of cylinder I through channel 5, chamber I1 in differential valve casing I5 and channel 21 into channel 9 where it augnents the volume of liquid discharged by pump 'l which at this time draws its supply of liquid through check valve II from its reservoir I0. Pump 1 thusv need only to supply a volume of liquid equal to the displacement of piston rod`3 so that piston 2 is moved upward at high speed.

When piston 2 reaches its upper limit, pump 1 is stopped or the displacement thereof is redu'ced to zero, piston 2 will come to rest, spring 39 lwill movevalve member 36 into contact with valve seat 35, and the pressure in the lower end of cylinder I will extend through the previously described channels to the lower end of bore 33 and cause plunger .38 to hold valve member 36 firmly against seat 35 to thereby prevent piston 2 from descending as previously explained.

The invention herein set forth is susceptible of various modifications and adaptations without departing' from the scope thereof as hereafter claimed.

The invention is hereby claimed as :follows:

l. ln a machine having an elementconstantly urged in one direction, the combination of a hy- `draulic motor connected to said element and having a rst port and a second port interchangeable for the admission and discharge of liquid to and from said motor, said element exerting upon said motor a force tending to operate it in one direction and cause it to discharge liquid through said second port, a pump connected to both of said ports, means for directing liquid from said pump to. said ports selectively to cause said motor to L move said element in opposite directions selectively, a valve for preventing the discharge of liquid through said second port and thereby causing thevforce exerted =by said element to create pressure in said motor, a piston operable by the pressure created by said element for holding said valve closed to prevent said motor from discharging liquid through said second port and thereby enabling said motor to hold said element stationary when said pump is ineective to energize said motor, and means operable in response to said pump delivering liquid to said nrst port `lor exhausting the pressure from said piston.4

2. In a machine having an element constantly Vurged in one direction, the combination of a hydraulic motor connected to said element and having a rst port and a second port interchangeable for the admission and discharge of liquid to and from said motor, said element exerting upon said motor a force tending to operate it in one direction and cause it to discharge liquid through said second port, a pump connected to both of said ports, means for directing liquid .by enable said motor to hold said element stationary when said pump is ineffective to energize said motor, and means responsive to said pump delivering liquid to said iirst port for rendering vsaid servo-motor ineffective to hold said valve closed.

3. In a machine having an element constantly urged in one direction, the combination of a hydraulic motor connected to said element and having a iirst port and a second port interchangeable for the admission and discharge of liquid to and from said motor, said element exerting upon said motor a force tending to operate it in one direction and cause it to discharge liquid through said second port, a pump connected to both of said ports, means for directing liquid from said pump to said ports selectively to cause said motor tofmove said element in opposlte'directions selectively, a spring loaded low pressure resistance valve connected to said second port to resist the discharge of liquid therefrom and thereby cause the force exerted by said element to create pressure at said second port, means including a pilot valve for causing'said pressure to apply sumcient additional loading to said resistance valve to posi-l tively hold it. closed against said pressure and thereby enable said motor to hold said element 22M-dgl@ stationary when said liquid directing nieans is inoperative, and means responsive to said pump delivering liquid to said rst port ior shifting said pilot valve to remove said additional loading iront.v said resistance valve.

e. in a machine having an element constantly urged in one direction, the combination of a hyd'raulic motor connected to said element and having a rst port and a second port interchangeable for the admission and discharge of liquid to and from said motor, said element exerting upon said motor a force tending to operate it in one direction and cause it to discharge liquid through said second port, a pump connected to both of said ports, means for directing liquid from said pump to said ports selectively to cause said motor to move said element in opposite directions selectively, a valve casing having a ybore and an annular valve seat communicating with said bore l at one end thereof, a valve member arranged within said bore and fitted to said valve seat, a plunger tted in said bore and having its adjacent end connected to said valve member, fluid channels connecting said valve seat and the part of said bore adjacent said valve seat in series between said pump and said second port, a light spring constantly urging said valve member against said seat to cause it to resist the discharge ofdiduld through said seat and thereby cause the force exerted by said element to create pressure at said second port, said valve member being smaller in diameter than said plunger to provide a shoucler therebetween so that said valve membei' is urged away from said seat by pressure created by said pump or by said element and acting upon said valve member or upon said shoulder, means including a valve for connecting the opposite end or said bore to said second port so that the opposite end of said plunger is subjected to the pressure created by saidelement and said plunger is caused to hold said valve member iirmiy against said seat to prevent liquid from being ejected through said second port and thereby enabling said motor to hold said element stationary when said liquid directing means is inoperative, said valve being adapted when shifted to connect said opposite bore end to drain to thereby prevent said plunger i'roin urging lsaid valve niernber against said seat, and ineans responsive to said pump delivering liquid to said first port for sluiting said valve to thereby permit the liduid discharged by said pump to energize said motor.

5. In a machine having a 'vertically movable element, the combination of a vertical cylinder, .a piston fitted in said cylinder and connected to said element, the weight or" said element tending to rnove said piston downward and cause it to eject liquid from the lower end of said cylinder, a pump, means for directing liquid from said pump to opposite ends of said cylinder selectively to ,cause said .piston to reciprocate said element,.a valve for preventing said piston freni ejecting liquid from the lower end of said cylinder and thereby causing the weight of said elenient to create pressure in the lower part of said cylinder, a piston operable by said pressure for holding said valve closed to prevent liquid from being ejected from the lower part of said cylinder and thereby enabling said pist/on to Support said element in a stationary position when said liquid directing means is inoperative, and means operable in response to said pump delivering liquid to the upper end of said cylinder for exhausting the pressure from said piston.

6. In a machine having a vertically movable element, the combination of a vertical cylinder,

a piston tted in said cylinder and connected toy a low pressure resistance valve connected t o the I lower end of said cylinder to resist the discharge of liquid therefrom and thereby cause the weight of said element to create pressure in lower end of said cylinder, a servo-motor for applying to said valve a closing force proportional to said pressure to hold said valve closed and thereby enable said piston to support said element in a stationary position when said vpump is inoperative, and means responsive to said pump delivering liquid to the upper end of said cylinder for rendering said servo-motor ineiective to hold said valve closed. i I

'7. In a machine having a vertically movable element, the combination of a vertical cylinder, a piston fitted in said'cylinder and connected to said element, the weight of said element tending to move said piston downward and cause it to eject liquid from the lower end of said cylinder, a pump, means for directing liquid from said pump to opposite ends of said cylinder selectively to cause said piston to reciprocate said element, a spring loaded low pressure ,resistance valve connected to the lower end of said cylinder to resist the discharge of liquid therefrom and thereby cause the weight of said element to create pressure in lower end of said cylinder, means including a pilot valve for causing said pressure to apply sumcient additional loading to said resistance valve to positively hold it closed against said pressure and thereby enable said piston to support said element in a stationary position when said liquid directingv means is inoperative, and means responsive to said pump delivering liquid to the upper end of said cylinder for shifting said pilot valve to remove said additional loading from said resistance valve.

8. In a hydraulic circuit including a motor, a'

pump for supplying liquid to said motor to enei-, gize the same, fluid channels connecting said pump to said motor and forming therewith a hydraulic circuit having a irst side and a second side, and means for reversing the flow in said circuit, the combination of a resistance valve connected into said rst side of said circuit, a

cylinder, a, piston arranged in said cylinder for urging said valve to its closed position, means including a pilot valve for connecting said cylinder to said iirst side of said circuit to thereby subject said piston to the pressure therein and cause it to hold said resistance valve closed, and means responsive to an increase in the pressure yin the second side of said circuit for shifting said pilot valve to exhaust the pressure from said piston.

9. In a machine having an element constantly urged in one direction, a hydraulic motor connected to said element to operate the same in opposite directions and having a first port and a `second port, said element exerting` upon said motor a force tending to cause it to discharge liquid throughsaid second' port, a pump, iluid channels connecting said pump to said ports to form with said motor a hydraulic circuit, and means `for reversing the flow in said circuit, the combination of a resistance valve connected bctween said second port and said pump to resist the discharge of liquid from said motor and thereby cause the force exerted by said element to create pressure at said second port, hydraulic means for holding said valve closed, means including a pilot valve for connecting said hydraulic 4means to said second port, and means for operating said pilot, valve in response to reversal of pressure in the opposite sides of said circuit.

10. In a hydraulic system for driving vin opposite directions a load which is constantly urged in one of said directions, the combination of a hydraulic motor connectedv to said load and having a rst port and a second port interchangeable for the admission and discharge of liquid to and from said motor, said load exerting upon said motor a force tending to operate it in a direction to cause it to discharge liquid through said second port, a pump, means for directing liquid from said pump to said ports selectively to cause said motor to drive said load in opposite directions selectively, a valve connected to said second port and adapted when closed to prevent thev discharge of liquid therefrom and thereby cause said loadto create pressure at said second port, a piston operable by be created at said second port, a piston connected to said valve and urged by said pressure in a direction to hold said valve closed, means for directing liquid.under pressure to said rst port, and means operable by the pressure at said rst port for causing the pressure at said second port to move said piston in a direction to open' said valve.

12. In a machine having an element urged in one direction by a substantially constant force, the combination of a hydraulic motor connected to said element and provided with interchangeable inlet and discharge ports, a pump, means for directing liquid from said pump to said ports alternately to cause said motor to move said element in opposite directions alternately, a valve adapted when eective to prevent the discharge of liquid from one of said ports to thereby prevent said elementvfrom' being moved by said force, and means responsive to the pressure at the other port reaching a given value for enabling the pressure at said one port to render said valve ineffective to prevent the dis harge of liquid from said motor. l

RICHARD E. DAVIS. 

